Respiratory treatment apparatus, such as a ventilator or positive pressure treatment device, may typically include a flow generator, an air filter, a mask, cannula or endotracheal tube, a supply tube connecting the flow generator to the mask or tube, sensors and a microprocessor-based controller. The flow generator may be a servo-controlled motor and an impeller (e.g., a blower). Optionally, the flow generator may also include a valve capable of discharging air to atmosphere as a means for altering the pressure delivered to the patient as an alternative to motor speed control of a blower. The sensors measure, amongst other things, motor speed, gas volumetric flow rate and outlet pressure, such as with a pressure transducer, flow sensor or the like.
Such devices have been automated for making changes to the system. For example, CPAP devices have been implemented to detect a condition of the patient. In U.S. Pat. No. 5,704,345 to Berthon-Jones, a device is described which automatically adjusts treatment pressure in response to indications of partial or complete upper airway obstruction. An automated procedure disclosed by Berthon-Jones involves detecting an open or closed patient airway by inducing airflow with a CPAP pressure generator that produces a modulated pressure output. The air flow induced by the pressure modulation is separated from air flow induced by other factors (such as heartbeat), by demodulating the measured air flow signal. Apneas are classified as “airway open” if the mean induced signal is more then 0.03 l/sec, and “airway closed” if the mean induced signal is less than 0.03 l/sec.
In the Patent Cooperation Treaty Published Patent Application No. WO2006/092001, Kwok describes a system of identifying masks by the use of a coded series of resistors. The controller may detect the mask by identifying a particular electrical resistance based on the resistors that is associated with the identity of particular masks.
It may be desirable for improved techniques and devices for assessing the state of such systems or controlling the operations thereof.